Field of the Invention
The present invention relates to the field of piezoelectric materials. More particularly, embodiments of the present invention relate to lead-free ceramic piezoelectric materials. Further embodiments provide a textured lead-free piezoelectric ceramic comprising of the system (Na0.5Bi0.5TiO3)—BaTiO3 (NBTBT) that uses Na0.5Bi0.5TiO3 (NBT) platelets as template seeds.
Description of Related Art
Piezoelectric materials find applications in a multitude of commonly used devices such as sensors, actuators and energy harvesters. However, most of these piezoelectric materials utilize lead-based compositions which are becoming a serious environmental problem owing to the restrictions imposed by regulatory agencies across the globe. See J. Rodel, W. Jo, K. T. P. Seifert, Eva-Maria Anton, T. Granzow and D. Damjanovic, J. Am. Ceram. Soc., 2009, 92, 1153. In the functional ceramics community, there is no problem more important than to find the replacement for lead-based piezoelectrics used for actuators. However, the electromechanical properties of actuators (high piezoelectric constant, high coupling factor, low loss, and high transition temperatures) for known lead-free compositions are far inferior to those of lead-based systems. See T. R. Shrout and S. J. Zhang, J. Electroceram., 2007, 19, 111.
Currently, there are two lines of thought for addressing this fundamental problem—(i) search for new compositions through computational models and experimental approaches (doping, solid solutions having morphotropic (M) or polymorphic (P) phase boundary (PB), and metastable phases in phase diagram), and/or (ii) improve the properties of known compositions through microstructural engineering and multilayering; where improving known compositions has been increasing in popularity.
The (Na0.5Bi0.5TiO3)—BaTiO3 (NBTBT) system has emerged as a potential candidate to replace lead-based piezoelectrics out of the various possibilities for lead-free systems. See Ben Wylie-van Eerd, Dragan Damjanovic, Naama Klein, Nava Setter, and Joe Trodahl, Phys. Rev. B, 2010, 82, 104112; Deepam Maurya, Cheol-Woo Ahn and Shashank Priya, Advances in Electroceramic Materials II: Ceramic Trans., 2010, 221, 47; Deepam Maurya, M. Murayama and Shashank Priya, J. Am. Ceram. Soc., 2011, 94, 2857 (“Deepam 2011”). A variety of research efforts have been pursued in literature towards improving the piezoelectric response of NBTBT. Most of these techniques, however, have been found to show limited success. See T. Takenaka, K. Maruyama, K Sakata, Jpn J. Appl. Phys., 1991, 30, 2236; P Fu, Z. Xu, R. Chu, W. Li, G. Zang, J. Hao, Mater. Sci. Engg. B, 2010, 167, 161; H. Li, C. Feng, P. Xiang, Jpn. J. Appl. Phys., 2003, 42, 7387; H. Li, C. Feng, W. Yao, Mater. Lett., 2004, 58, 1194; W. Lang, D. Xiao, L. Dunmin, Z. Jianguo, Y. Ping, L. Xiang, Jpn. J. Appl. Phys., 2007, 46, 7382; R. Zuo, C. Ye, X. Fang, J. Li, J. Eur. Ceram. Soc., 2008, 28, 871; X. X. Wang, H. Chan, C. L. Choy, Appl. Phys. A: Mater. Sci. Process., 2005, 80, 333; M. S. Yoon, Y. G. Lee, S. C. Ur, J. Electroceram., 2009, 23, 564. Driving the material through electric-field induced phase transformation in compositions of NBTBT that exhibit structural instabilities can provide large strain but this is not practical for applications due to the intrinsic non-linear behavior and high amplitude of electric drive.
It is known that the piezoelectric properties of perovskites can be drastically enhanced by imparting crystallographic texture, a process known as texturing. See Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya and M. Nakamura, Nature, 2004, 432, 84 (“Y. Saito”); See S. Kwon, E. M. Sabolsky, G. L. Messing, S. Trolier-McKinstry, J. Am. Ceram. Soc., 2005, 88, 312 (“S. Kwon”). Texturing enables the polycrystalline ceramics to resemble their single crystal counterparts so that favorable domain engineered states can be obtained. However, texturing of lead-free compositions is an extremely challenging problem due to several fundamental constraints such as volatility of alkali elements, chemical reactivity with seed templates, poor sinterability of the base compositions, and cubical equilibrium grain shape.
Therefore, there exists a need to provide a lead-free ceramic material that still maintains the desired characteristics comparable to ceramics containing lead. Moreover, there exists a need of improving the method through which synthesis of textured lead-free ceramic compositions can be conducted in order to provide piezoelectric properties that closely mimic domain engineered single crystals.